1. Field of the Invention
The invention relates to a disc brake caliper having a bracket that stiffens the rectangular shaped aperture within the caliper against the parallelogram effect.
2. Background Information
Friction brakes are used in cars, trains, airplanes, elevators, and other machines. For each wheel of an automobile, conventional disk-type brakes include two opposing steel plates, each faced with a heat- and wear-resistant lining known as a brake pad. Between a pair of brake pads is a brake rotor that rotates as the axle of the automobile turns from power transmitted by an engine. The brake rotor provides two heat dissipating surfaces, against which a pair of brake pads may be applied so as to slow a vehicle down or bring it to rest through controlled slippage. The brake rotor is formed of two annular rings, within which are radially extending channels that force air from the interior surface of the rings to the exterior surface of the rings. The passing air draws heat from the brake rotor and expels it radially outward in the direction of the moving brake rotor.
To apply the steel plate backed brake pads against the brake rotor, each plate is backed by two hydraulic pistons that cause the plates to move in the axial direction. These pistons are housed in cylindrical piston bores located in two C-shaped (or U-shaped) bodies. Each C-shaped body includes two arms extending from a base that supports the piston bores. When the two C-shaped bodies are bolted together, an access aperture is formed as the middle of a rectangular shape formed by the two C-shaped bodies. This aperture permits installation and removal of the brake pads from a position that is radially above the axle of the automobile. The device consisting of the two plates lined with a frictional material that is pressed against the sides of the brake rotor (or "disc") is known as a disc brake caliper.
In order to slow or stop an automobile, a driver steps on a brake pedal. Movement of the brake peddle operates a valve that allows one side of a piston to be exposed to atmospheric pressure, while engine-intake manifold vacuum is applied to the other side of that piston. This great difference in pressure causes the piston to move. This movement is transmitted through high hydraulic pressure to the pistons disposed about each opposing pair of brake pads. As pedal pressure is applied by the driver, the brake pads are forced against each surface of the rotating brake rotor by these pistons. The friction interface between the pads and the rotor surface slows the vehicle down or brings it to rest through controlled slippage.
During the friction interface between the brake pads and the disc rotor, a variety of forces work against the rectangular shape of the caliper in an effort to distort this shape. For example, the hydraulic pressure applied within the piston bores against the pistons works to distort the cylindrical shape of the bore. This hydraulic pressure also presses against each caliper plate so as to push each place in the axial direction. Since brakes primarily are applied as an automobile is traveling, there is a torque reaction in the direction of rotation of the brake rotor that is applied against an internal face of one pair of opposing arms of the plates. Conventionally, this internal face includes a stainless steel surface that permits the brake pads to slide smoothly on the internal surface of that leading end.
The force against the stainless steel surface in a rectangular shape caliper causes the caliper to act like a four-bar linkage out of the rectangular shape with the stainless steel surface posing as a fixed linkage. The variety of forces developed within the caliper work to rotate this four-bar linkage in one direction or another so that the internal right angles of the rectangular shape become the obtuse and acute angles of a parallelogram. However, due to the rigidity of the C-shaped bodies and the uneven application of the forces developed within the caliper, the rectangular shape caliper design actually becomes S-shaped as a result of this parallelogram effect. The S-shape becomes especially pronounced at the trailing end of the caliper.
The parallelogram effect results in unusual wear on the surfaces of the brake pads. This unusual wear not only decreases the overall performance of the brake pads, but increases the vibration noise emanating from the brake pads just after the pads separate from the brake rotor. This makes it more difficult for automobiles to meet federal Noise Vibration of Harshness (NVH) standards. Thus, what is needed is a device to stiffen the rectangular shape within the caliper against the brake torque reaction forces resulting in the parallelogram effect.